The quantitative analysis mode of DFRA on/off gain with multiple localized loss in fiber is deduced from the non-depletion simple Raman approximate equations based on co-propagating pump （or back pump）

then

the quantitative analysis mode is modified based on the fiber formed by varied fiber length with multiple localized loss between them and varied Raman gain efficiency of each varied fiber. The mode is modified in DWDM system while considering the multiple localized loss affect the signal-to-signal stimulated and spontaneous Raman scattering gain. In order to check the validity and the applicability of the above mentioned two modes. The quantitative analysis expression of the two modes whose error do not exceed 0.02dB （compared to reference [3] and [4] that only show qualitative analysis） has been validated by simulated back-pumped fiber Raman amplifier with multiple signal and pump channels whose system of coupled equations has taken into account pump-to-pump

pump-to-signal

and signal-to-signal stimulated and spontaneous Raman scattering. The profitable conclusion can be deduced: the on/off gain of the DFRA with one splice loss less than 0.092dB per 3km

（the whole length does not exceed 120km） will not descend to the 90% on/off gain of the DFRA with no splice. The result shows that it is feasible to apply DFRA to the paved fiber system. The two modes of this paper can be used as real DFRA system design reference.